Chronic stress is detrimental to one's health and can lead to many stress-based or stress-induced diseases. The difficulty in managing stress, from both a clinical and societal perspective, is that stress is difficult to quantify—what is stressful for one person may not be for another. Some stress is essential in life and, in healthy amounts, stress can provide motivation to accomplish goals. Sometimes stress is necessary in order for the body to protect itself and to overcome obstacles. But the long-term effects of prolonged physiological and psychological stress can and will cause the body harm.
A number of different techniques exist for determining the stress level of a subject. Example techniques include, for example, heart rate variability (HRV) analysis, biological impedance analysis (BIA), body surface temperature analysis, body core temperature analysis, muscle twitch analysis, and respiratory rate analysis.
Heart rate variability (HRV), for example, is a measure of the fluctuations of the heartbeat. Even the beats of a resting heart rate are not perfectly routine or rhythmic, with some variability in the heartbeat frequency. Study of this heartbeat variability is a non-invasive technique providing information about both parasympathetic and sympathetic activity within a subject. Although there are limitations, simple time and frequency domain techniques are commonly used to give quantitative measures allowing implications about stress to be understood.
BIA relies upon skin impedance to analyze a subject's stress. Body surface and body core temperature analysis rely upon body temperatures to analyze a subject's stress. Muscle twitch analysis involves detecting muscle twitch within a subject to analyze stress and respiratory rate analysis looks at a subject's respiratory rate to determine stress.
Although these techniques provide some methods for analyzing a subject's stress, no devices exist that automatically use these techniques to determine a user's stress.